Well I am one of those anal people who loves to keep their engine bay clean. I do it for a couple of reasons, one being that it just looks great and the second is to make it easier to do work under there (no oil/grease buildup).
I would take a look at this Engine Bay Cleaning
as it might help answer some questions you might have.
If you start keeping the engine/engine bay clean early on a new car it just makes it that much easier in the long run.
I hope this helped somewhat.